1. Field of the Invention
The present invention relates to a method for reusing a resource for designing an operational amplifier, and to an operational amplifier, a layout generating apparatus and a layout generating program which can realize the method of reuse.
2. Description of the Background Art
When designing an operational amplifier, a designer determines various circuit constants such as the bias voltage, the size of each transistor (the gate width and the gate length) etc., to satisfy required characteristics such as the maximum operating frequency, slew rate, etc., and designs the layout pattern including circuit elements and interconnections which constitute the operational amplifier. In order to efficiently design the operational amplifier, existing design resources are reused when the specifications are changed.
In conventional reuse of design resources for operational amplifiers, the designer conducts a simulation and determines circuit constants such as the shrink factor (reducing scale), bias voltage, etc. so that the required characteristics are satisfied, and varies the layout pattern design of the operational amplifier.
In the conventional operational amplifier design resource reuse method, however, the circuit constants have so wide a choice that determining the circuit constants is a time-consuming work. Changing the layout pattern design is also time-consuming since the designer cannot achieve it by selecting an appropriate layout pattern out of a plurality of prepared layout patterns.
An object of the present invention is to provide a method for reusing a resource for designing an operational amplifier which can easily reuse an existing design resource and which can shorten the time required for the reuse, and an operational amplifier, a layout generating apparatus, and a layout generating program which can realize the method of reuse.
According to an aspect of the present invention, a method for reusing a resource for designing an operational amplifier comprises the steps of: preparing different sets of layout information for an operational amplifier comprising a plurality of transistors, the plurality of transistors having their channel widths varied by different factors among the different sets of operational amplifier layout information; and selecting one of the different sets of operational amplifier layout information and determining the value of a bias current of the operational amplifier so that a required characteristic is satisfied.
The method of reuse of the invention thus prepares different sets of operational amplifier layout information, where the channel widths of the plurality of transistors are varied in a uniform manner. Then one of the different sets of operational amplifier layout information is selected and the value of the bias current of the operational amplifier is determined, so as to design an operational amplifier which satisfies a required characteristic. An existing design resource can thus be easily reused and the time required for the reuse can be shortened.
The operational amplifier may have a circuit configuration in which a bias voltage generated by a bias generating circuit is applied to a transistor serving as a current source of the operational amplifier, thereby supplying a current corresponding to a constant multiple of a bias current of the bias generating circuit as a bias current of the operational amplifier, and the method of reuse may further comprise a step of previously setting a relation between the value of the bias current of the operational amplifier represented by the different sets of layout information and the value of the bias current of the bias generating circuit so that a set of operational amplifier layout information can be uniquely selected from the different sets of operational amplifier layout information and the value of the bias current of the bias generating circuit can be uniquely determined on the basis of the value of the bias current of the operational amplifier which satisfies the required characteristic.
In this case, the operational amplifier layout information can be uniquely selected from the different sets of operational amplifier layout information and the value of the bias current of the bias generating circuit can be uniquely determined. This remarkably reduces the work load and the time required for optimization to obtain the operational amplifier layout information which satisfies the required characteristic.
The operational amplifier design resource reuse method may further comprise a step of previously setting the different factors and the value of the bias current of the bias generating circuit so that the bias current of the operational amplifier continuously varies.
In this case, since the bias current of the operational amplifier can be continuously varied by varying the bias voltage of the bias generating circuit at each factor, one of the different sets of operational amplifier layout information and the value of the bias current of the operational amplifier can be easily selected and determined to satisfy the required characteristic.
The operational amplifier design resource reuse method may further comprise the steps of determining an upper limit of a bias voltage applied to a transistor serving as a current source of the operational amplifier on the basis of an output voltage range, and determining a lower limit of the bias voltage on the basis of cutoff of the transistor serving as a current source. This enables an optimum bias voltage to be selected.
It is preferred that the different factors include three or four kinds of factors. This remarkably reduces the design time for preparing the different sets of operational amplifier layout information corresponding to the different factors.
The plurality of transistors may further comprise a pair of transistors having a differential configuration and the transistor serving as a current source may supply a current to the pair of transistors. Also, each of the plurality of transistors may comprise a field-effect transistor.
According to another aspect of the invention, an operational amplifier comprises: a plurality of transistors including a transistor serving as a current source; a bias generating circuit that applies a bias voltage to the transistor serving as a current source; and a channel width varying circuit that varies channel widths of the plurality of transistors, thereby realizing a method for reusing a resource for designing an operational amplifier comprising preparing different sets of layout information for an operational amplifier comprising a plurality of transistors, the plurality of transistors having their channel widths varied by different factors among the different sets of operational amplifier layout information, and selecting one of the different sets of operational amplifier layout information and determining the value of a bias current of the operational amplifier so that a required characteristic is satisfied.
In the operational amplifier of the invention, the channel widths of the plurality of transistors can be varied by the channel width varying circuit, so that the operational amplifier design resource reuse method can be realized easily.
The operational amplifier may further comprise a bias voltage adjusting circuit that adjusts the bias voltage generated by the bias generating circuit.
In this case, the bias voltage can be adjusted by the bias voltage adjusting circuit, while the channel widths of the plurality of transistors can be varied by the channel width varying circuit. Then the operational amplifier design resource reuse method can be realized more easily.
The plurality of transistors may further include a pair of transistors having a differential configuration and the transistor serving as a current source may supply a current to the pair of transistors. Also, each of the plurality of transistors may comprise a field-effect transistor.
According to a further aspect of the invention, an operational amplifier comprises: a plurality of transistors including a transistor serving as a current source; a bias generating circuit that applies a bias voltage to the transistor serving as a current source; and a bias voltage adjusting circuit that adjusts the bias voltage generated by the bias generating circuit, thereby realizing a method for reusing a resource for designing an operational amplifier comprising preparing different sets of layout information for an operational amplifier comprising a plurality of transistors, the plurality of transistors having their channel widths varied by different factors among the different sets of operational amplifier layout information, and selecting one of the different sets of operational amplifier layout information and determining the value of a bias current of the operational amplifier so that a required characteristic is satisfied.
In the operational amplifier of the invention, the bias voltage can be adjusted by the bias voltage adjusting circuit, so that the operational amplifier design resource reuse method can be realized easily.
The plurality of transistors may further include a pair of transistors having a differential configuration and the transistor serving as a current source may supply a current to the pair of transistors. Also, each of the plurality of transistors may comprise a field-effect transistor.
According to another aspect of the invention, an operational amplifier comprises: a plurality of transistors including a transistor serving as a current source; a bias generating circuit that applies a bias voltage to the transistor serving as a current source; and a channel width varying circuit that varies channel widths of the plurality of transistors.
In the operational amplifier of the invention, the channel widths of the plurality of transistors can be varied by the channel width varying circuit. It is then possible to prepare different sets of operational amplifier layout information in which a plurality of transistors of the operational amplifier have their channel widths varied by different factors among the different sets of layout information, and then select one of the different sets of operational amplifier layout information and determine the value of the bias current of the operational amplifier, so as to satisfy a required characteristic. The operational amplifier design resource reuse method can thus be realized easily.
According to a further aspect of the invention, an operational amplifier comprises: a plurality of transistors including a transistor serving as a current source; a bias generating circuit that applies a bias voltage to the transistor serving as a current source; and a bias voltage adjusting circuit that adjusts the bias voltage generated by the bias generating circuit.
In the operational amplifier of the invention, the bias voltage can be adjusted by the bias voltage adjusting circuit. It is then possible to prepare different sets of operational amplifier layout information in which a plurality of transistors of the operational amplifier have their channel widths varied by different factors among the different sets of layout information, and then select one of the different sets of operational amplifier layout information and determine the value of the bias current of the operational amplifier, so as to satisfy a required characteristic. The operational amplifier design resource reuse method can thus be realized easily.
According to another aspect of the invention, an operational amplifier layout generating apparatus comprises: first input means for entering a characteristic required for an operational amplifier; second input means for entering different sets of layout information for the operational amplifier, the operational amplifier comprising a plurality of transistors, the plurality of transistors having their channel widths varied by different factors among the different sets of operational amplifier layout information; third input means for entering a relation between the value of a bias current of the operational amplifier represented by the different sets of layout information, and the different factors and the value of a bias current of a bias generating circuit; determining means for determining the bias current of the operational amplifier on the basis of the characteristic entered through the first input means; selecting means for determining the bias current of the bias generating circuit and selecting one of the different sets of operational amplifier layout information entered through the second input means on the basis of the relation entered through the third input means and the bias current of the operational amplifier determined by the determining means; executing means for executing a simulation about the operational amplifier using the set of operational amplifier layout information selected by the selecting means; and output means for outputting the layout information selected by the selecting means when a result of the simulation executed by the executing means satisfies the characteristic entered through the first input means.
In the operational amplifier layout generating apparatus of the invention, the first input means enters a characteristic required for an operational amplifier; the second input means enters different sets of layout information for the operational amplifier, where a plurality of transistors of the operational amplifier have their channel widths varied by different factors among the different sets of operational amplifier layout information; and the third input means enters a relation between the value of a bias current of the operational amplifier represented by the different sets of layout information, and the different factors and the value of a bias current of a bias generating circuit. Then, first, the determining means determines the bias current of the operational amplifier on the basis of the characteristic entered through the first input means. Next, the selecting means determines the bias current of the bias generating circuit and selects one of the different sets of operational amplifier layout information entered through the second input means on the basis of the relation entered through the third input means and the bias current of the operational amplifier determined by the determining means. Then the executing means executes a simulation about the operational amplifier using the set of layout information selected by the selecting means. When the results of the simulation executed by the executing means satisfy the characteristic entered through the first input means, the output means outputs the operational amplifier layout information selected by the selecting means.
The operational amplifier layout information which satisfies the required characteristic is thus automatically outputted, so that existing design resources can be easily reused and the time required for the reuse can be shortened.
A further aspect of the invention is directed to a layout generating program for generating a layout for an operational amplifier, wherein the layout generating program can be read by a computer, and the layout generating program causes the computer to execute a process comprising: accepting an input of a characteristic required for an operational amplifier; accepting an input of different sets of layout information for the operational amplifier, the operational amplifier comprising a plurality of transistors, the plurality of transistors having their channel widths varied by different factors among the different sets of operational amplifier layout information; accepting an input of a relation between the value of a bias current of the operational amplifier represented by the different sets of layout information, and the different factors and the value of a bias current of a bias generating circuit; determining the bias current of the operational amplifier on the basis of the entered characteristic; determining the bias current of the bias generating circuit and selecting one of the entered different sets of operational amplifier layout information on the basis of the entered relation and the determined bias current of the operational amplifier; executing a simulation about the operational amplifier using the selected set of operational amplifier layout information; and outputting the selected operational amplifier layout information when a result of the simulation satisfies the entered characteristic.
According to the operational amplifier layout generating program of the invention, first, the bias current of the operational amplifier is determined on the basis of the entered characteristic. Next, the bias current of the bias generating circuit is determined and one of the different sets of operational amplifier layout information is selected on the basis of the entered relation and the determined bias current of the operational amplifier. Further, a simulation about the operational amplifier is executed by using the selected set of layout information. When the results of the simulation satisfy the entered characteristic, the selected operational amplifier layout information is outputted.
The operational amplifier layout information which satisfies the required characteristic is thus automatically outputted, so that existing design resources can be easily reused and the time required for the reuse can be shortened.
According to another aspect of the invention, an operational amplifier layout generating apparatus comprises: a first input device that enters a characteristic required for an operational amplifier; a second input device that enters different sets of layout information for the operational amplifier, the operational amplifier comprising a plurality of transistors, the plurality of transistors having their channel widths varied by different factors among the different sets of operational amplifier layout information; a third input device that enters a relation between the value of a bias current of the operational amplifier represented by the different sets of layout information, and the different factors and the value of a bias current of a bias generating circuit; a processing unit that determines the bias current of the operational amplifier on the basis of the characteristic entered through the first input device, determines the bias current of the bias generating circuit and selects one of the different sets of operational amplifier layout information entered through the second input device on the basis of the relation entered through the third input device and the bias current of the operational amplifier determined by the determining device, and executes a simulation about the operational amplifier using the selected set of operational amplifier layout information; and an output device that outputs the selected layout information when a result of the simulation executed by the processing unit satisfies the characteristic entered through the first input device.
In the operational amplifier layout generating apparatus of the invention, the first input device enters a characteristic required for an operational amplifier, the second input device enters different sets of layout information for the operational amplifier, where a plurality of transistors of the operational amplifier have their channel widths varied by different factors among the different sets of operational amplifier layout information; and the third input device enters a relation between the value of a bias current of the operational amplifier represented by the different sets of layout information, and the different factors and the value of a bias current of a bias generating circuit. First, the processing unit determines the bias current of the operational amplifier on the basis of the characteristic entered through the first input device. Next, the processing unit determines the bias current of the bias generating circuit and selects one of the different sets of operational amplifier layout information entered through the second input device on the basis of the relation entered through the third input device and the bias current of the operational amplifier determined by the processing unit. Then the processing unit executes a simulation about the operational amplifier using the set of operational amplifier layout information selected by the processing unit. When the results of the simulation executed by the processing unit satisfy the characteristic entered through the first input device, the output device outputs the selected operational amplifier layout information.
The operational amplifier layout information which satisfies the required characteristic is thus automatically outputted, so that existing design resources can be easily reused and the time required for the reuse can be shortened.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.